Several hundred people, including survivors of the Jasenovac camp, victims' relatives, officials, religious leaders and foreign diplomats gathered for a multi- denominational service and wreath-laying ceremony at the camp site.
"The horrors of Jasenovac warn us... Not to allow discrimination and persecution based on national, religious, ideological or gender differences ever again," parliamentary speaker Josip Leko said.
Prime Minister Zoran Milanovic said the country, which has been independent since 1991, had distanced itself in its constitution from the pro-Nazi Ustasha regime which set up the camp in 1941.
The ceremony marked the 70th anniversary of an attempted escape by around 600 inmates from the camp. Only around 90 survived, with the others killed by guards.
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The ceremony at Jasenovac, known as 'Croatia's Auschwitz,' is held every year on the Sunday closest to April 22.
The camp, around 100 kilometres southeast of Zagreb, was dismantled a few days after the failed breakout.
The total number of people killed there - mostly Serbs, Jews, Roma and anti-fascist Croatians - remains disputed, varying from 70,000 to 700,000, according to Serbian figures.